Gastrolepta anthracina

Body length 6 to 8.5 mm. Overall appearance is of a very smart, slim, black and white fly. The thorax is black with two white 'shoulder' stripes and the abdomen is black with white, or greyish-white bands at the start of each tergite. In this species the abdomen is slightly shorter than the head+thorax, less heavily bristled; head proportionally quite wide compared to the thorax with a long, sloped frons, giving a “streamlined” profile.

https://tachinidae.org.uk/blog/identifying-slim-black-tachinids-with-grey-dusting/

with a quality image showing the relevant features

Unless identified by a recognised expert, a photo is required, and the specimen should be examined with a microscope. In the comments box, state the key or ID method used and describe the size and identifying characters.

Woodland edge and hedgerows. 

Late May to August.

It is thought that its host species is the Darkling Beetle, Lagria hirta.

In Britain this species in found mostly around southern coasts and in south-eastern England.

Status in Leicestershire and Rutland not known.